1. Field of the Invention
The present invention relates to a USB (Universal Serial Bus) power adapter and more particularly to a USB power adapter capable of receiving power from AC and DC power sources.
2. Description of the Related Art
Latest electronic products, such as notebook computers, mobile phones, MP3 players and the like, become more and more diversified with widespread marketplace acceptance. Those electronic products are supplied by batteries to acquire their operating power, and the batteries are charged by chargers connected to AC power sources or through the power pins of USB ports of other electronic products. Although electronic products can be charged through charging ports or USB ports with compatible specifications, right types of chargers are needed to correspond to the connected power sources. For example, an AC to DC charger should be prepared at home or in the office to convert the 110V AC power into 5V DC power, and a DC to DC charger should be prepared in a vehicle to convert 12V or 24V DC power to 5V DC power. Hence, inconvenience arises because users need to purchase or carry various chargers for desired voltage types. Conventional universal chargers are equipped with replaceable plugs to correspond to various AC receptacles or vehicle power sockets. However, it is still inconvenient for users to carry many different types of plugs for the purpose of operation.